1. Field of the Invention
The present invention relates to a thin film transistor (TFT), and more particularly, to an oxide TFT having excellent properties and improved reliability and an array substrate including the oxide TFT.
2. Discussion of the Related Art
As the society has entered an information age, a field of display devices that represent all sorts of electrical signals as visual images has developed rapidly. Particularly, the liquid crystal display (LCD) device or the organic light emitting diode (OLED) display device as a flat panel display device having characteristics of light weight, thinness and low power consumption is developed to be used as a substitute for a display device of cathode-ray tube type.
Since the LCD device including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely used.
On the other hand, since the OLED device has excellent characteristics of high brightness, a low power consumption and high contrast ratio, the OLED display device has been widely used. Moreover, the OELD display device has advantages of a high response rate, a low production cost and so on. The OLED does not require a backlight such that thin and light-weight device is provided.
Both the LCD device and the OLED display device require a thin film transistor (TFT) as a switching element for controlling on and off of each pixel region. In addition, the OELD device requires another TFT as a driving element for driving an emitting diode in each pixel region.
The TFT including a semiconductor layer of amorphous silicon has been widely used.
Recently, to meet requirements of large size and high resolution, the TFTs having faster signal process, more stable operation and durability is required. However, the TFT using amorphous silicon has a relatively low mobility, e.g., less than 1 cm2/Vsec, there is a limitation for the large and high resolution OLED display device.
Accordingly, an oxide TFT including an active layer of an oxide semiconductor material, which has an excellent electrical property, e.g., mobility and off-current, is introduced.
FIG. 1 is a cross-sectional view of the related art oxide TFT.
As shown in FIG. 1, the oxide TFT includes a gate electrode 21, a gate insulating layer 30, an oxide semiconductor layer 40, an etch-stopper 50, a source electrode 62 and a drain electrode 64.
The gate electrode 21 is formed on a substrate (not shown). The gate insulating layer 30 covers the gate electrode 21.
The oxide semiconductor layer 40 is formed on the gate insulating layer 30 and corresponds to the gate electrode 21. The oxide semiconductor layer 40 is formed of an oxide semiconductor material.
The etch-stopper 50 is formed on the oxide semiconductor layer 40 and corresponds to a center of the oxide semiconductor layer 40. Since the oxide semiconductor layer is easily damaged by an etchant for etching a metal layer for the source and drain electrodes 62 and 64, the oxide semiconductor layer 40 is protected by the etch-stopper 50. Both ends of the oxide semiconductor layer 40 are exposed.
The source and drain electrodes 62 and 64 are respectively connected to both ends of the oxide semiconductor layer 40 and are spaced apart from each other.
The TFT includes the oxide semiconductor layer 40 such that the properties of the TFT are improved.
However, the oxide semiconductor layer 40 is easily damaged by light. When the oxide TFT is used for the LCD device, the oxide semiconductor layer 40 is exposed to the ambient light. When the oxide TFT is used for the OLED display device, the oxide semiconductor layer 40 is exposed to the ambient light and the light from the emitting diode. As a result, the properties of the oxide TFT are degraded.